Overuse of drugs in animal farming linked to growing antibiotic-resistance in humans

Urgent calls from health experts to reduce antibiotic use on intensive farms are largely resisted by the agribusiness food lobby, who downplay its role in the spread of antibiotic resistance in humans. Tom Levitt reports

It is described as the most 'serious global crisis' yet in the farming industry no-one is talking in such terms.

Around one half of all antibiotics in Europe are prescribed for animals - the figure in the rest of the world is estimated to be even higher. In the US, where it is reported to account for 70 per cent of antibiotic use, one medical specialist recently said its use in humans 'pales in comparison' to its use in the agri-food industry.

The overuse comes at a cost as it contributes to an ever-increasing amount of antimicrobial resistance as bacteria evolve to withstand existing antibiotics. What's more there is now evidence these resistant bacteria are being transferred to humans via the food chain - putting us at risk of more untreatable infections.

Bacteria can spread from animals to humans through a number of ways, including infected faeces contaminating animals during the slaughter process or being spread as manure on crops.

The World Health Organisation (WHO) says drug use in farm animals plays a 'significant role' in spreading antibiotic-resistant salmonella and campylobacter infections in humans while EU food safety officials say it could also be a source of some antibiotic-resistant strains of MRSA and E.coli - both potentially life-threatening infections - and, in the case of E.coli, a new highly resistant type of which was recently found on a large number of dairy, pig and poultry farms in England and Wales.

Dutch scientists recently went as far as estimating that between a third and one half of resistance in human infections in the Netherlands originated from farm animals. Although the figure is estimated to be lower in the UK, agriculture is believed to now account for the majority of antibiotic-resistance in food poisoning cases.

Despite this concern, efforts to reduce the use of antibiotics in animals, particularly on intensive pig and poultry farms, remain muted.

One health expert, writing for the WHO, likens the situation to overfishing or the overgrazing of cattle on common grass. The continued overuse of antibiotics is being followed by a growing resistance as the bacteria evolve to withstand the effect and presence of the antibiotic. And it's getting worse, with fewer new antibiotics becoming available and resistance continuing to rise. Just like diminishing fish stocks or lack of grass on the common land, overuse by one person will mean we all stand to lose out. Although as others have pointed out, while fisheries can restock and grass re-grow, bacteria don't disappear.A history of overuse

In the UK, government vets estimated that 350 tonnes of antibiotics were used on farm animals in 2009. The vast majority, 95 per cent or more, in the pig and poultry sectors and the rest largely in dairy farming. In the US, antibiotics are also used in low levels as growth promoters in the cattle sector, a practice banned in Europe in 2006. Small sub-therapeutic doses have been found to improve the growth rates of farm animals. But as they only limit the spread of bacteria rather than killing it, they are seen as a major factor in the spread of antibiotic-resistance.

Although officially opposed to the use of antibiotics as growth promoters, government officials in the US have repeatedly shied away from banning their use. A proposed ban on one such class of drugs cephalosporins in 2008 was quietly dropped after strong opposition from the pharmaceutical and agri-food industry. This was despite the government saying at the time that the use of the drugs posed a risk to humans, with evidence of resistance spreading from animals through foodborne bacteria.

In Europe the use of antibiotics as growth promoters may be banned but the antibiotics themselves are still able to be prescribed by a vet. For example, sales of tetracyclines, previously used as a growth promoter (still is in the US), remained at 45-55 per cent of antimicrobial sales to farmers in the UK in each year from 2004 to 2009.

'Downplaying' of problem

Many point the blame for the high use of antibiotics at intensive farming techniques. They say it is no surprise that the two biggest users are the pig and poultry sectors, here thousands of animals are reared in cramped areas where infection can spread quickly. Rather than to treat sick animals, antibiotics are added to the feed to ward off infection during the animals short lifespan.

In some cases, particularly broiler chickens and pigs where they are subjected to a herd treatment rather than as individuals, the animals can be exposed to antibiotics for most of their lifespan. UK scientists say the misuse of antibiotics in intensive chicken farms had allowed salmonella in particular to spread, with the antibiotics acting as masking agents for proper sanitation and the confined housing allowing germs to spread rapidly through the chickens.

Although the National Farmers Union (NFU) say there is no evidence more intensive farming systems use more antibiotics, a UK government study published in 2006 found the use of antimicrobial drugs on organic farms was far lower (and often zero) than on conventional farms. Unsurprisingly, the farms administering the highest quantities of drugs were the large conventional pig and poultry units.

Campaign groups like the Soil Association say both the farming industry and government are downplaying the need to dramatically reduce antibiotic use in farm animals. As such they are a block on efforts to stop the spread of more antibiotic-resistant infections in both animals and humans.

Officially, the Food Standards Agency (FSA) suggests the transfer of resistance from food animals to humans is only likely to be a 'minor' contributor to antibiotic-resistance in humans. Just like the industry-led Responsible Use of Medicines in Agriculture Alliance (RUMA), it makes no demand to reduce antibiotic use in farming.

In fact, like the US, the UK has deliberately shied away from attempts to reduce antibiotic-use in farming. Earlier this year the government blocked moves to ban the direct promotion of antimicrobial medicines to farmers. The Government's own veterinary officials had proposed the ban, with the support of professional vets, who argued it would reduce the pressure being placed on them by farmers to prescribe antibiotic drugs unnecessarily. The vets said the adverts did not help farmers make informed decisions and that it was time to end the 'heavy advertising' of new antimicrobials by drug companies. After strong opposition from farming groups, the government rejected the vets advice and dropped the proposal.

Campaigners were left aghast, saying the adverts continued a culture of farmers seeing antibiotics as the first answer to tackling the problem. 'There has been little public scrutiny of farm antibiotic use for over a decade, yet during that time we have seen farmers dramatically increase their use of antibiotics classified by the WHO as ‘critically important in human medicine’ and we have also seen the development of several serious antibiotic-resistant bugs in farm animals which are passing to humans on food and in other ways. It is high time that the government took this problem seriously,' said Soil Association policy advisor Richard Young.

In a positive sign, there are indications the EU will try to bring in tougher regulations as part of its new animal health strategy, due later this year. MEPs recently called for a crackdown on antibiotic use saying food was emerging as, 'an important vector for transmitting antimicrobial resistance through antibiotic residue in meat'. They said it was time for a more 'rational use' of antibiotics by farmers, which would mean greater focus on alternatives such as improved hygiene, vaccination and breeding for resistance.

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